1. Field of the Invention
This invention relates to a method for preparing golf balls having a multi-layer cover using an injection mold.
2. Prior Art
Golf balls of interest have a core and a cover which consists of inner and outer covers. One prior art injection molding method for forming the inner cover is illustrated in FIGS. 10 and 11. A prior art injection mold 1 is illustrated as comprising a pair of separable upper and lower mold segments 2 and 3 which define a spherical cavity 4 when mated along a parting surface. The mold also includes a plurality of upper and lower support pins 6 and a plurality of gates (not shown) extending along the parting surface or in proximity to the parting surface in the event of tunnel gates. The support pins 6 are received in holes 6a for vertical motion. The mold further includes vertically extending holes 9 and stationary cylindrical pins 10 which are received in the holes 9 to define degassing gaps with the inner surface of the holes 9.
Upon use, a preformed core 5 is placed in the mold cavity as an insert and supported in place by the upper and lower support pins 6 as shown in FIG. 10. A cover stock for the inner cover is injected into the space between the mold cavity 4 and the core 5 through the gates. Immediately before injection of the cover stock or simultaneous with the completion of injection, the support pins 6 are withdrawn so that the distal ends of the support pins 6 become flush with the cavity surface or molding surface 7. In this way, a inner cover 8 is formed around the core 5 as shown in FIG. 11.
Then the molded part is removed from the mold. Using another injection mold of substantially the same construction as above except that the molding surface is provided with a negative dimple pattern. The molded part is supported in place in the mold cavity and a cover stock for the outer cover is injection molded by the same procedure described above. A final molded part or golf ball is obtained in this way. In an alternative procedure, the outer cover is formed by compression molding.
While the outer cover is formed by injection molding or compression molding, a particular combination of the inner and outer cover materials can provide poor adhesion of the outer cover to the inner cover so that the ball becomes less durable. For the purpose of increasing adhesion, the inner cover must be mechanically roughened or chemically treated on the surface. This mechanical roughening or chemical treatment adds one step to the process although the adhesion between the outer cover and inner cover is enhanced thereby.